Lens mirror array, optical unit and image forming apparatus

ABSTRACT

An example is a lens mirror array in which a plurality of optical elements, which comprises a first lens surface formed at the top of convex portion protruding outwards for converging light, a protrusion which includes a first mirror surface that reflects the light emitted from the first lens surface at the top and a light-shielding surface that has side walls at two sides thereof with respect to a light advancing direction and prevents advance of the light through the side walls, a second mirror surface that reflects the light reflected by the first mirror surface of the protrusion and a second lens surface that images the light emitted from the second mirror surface on an image plane, is arranged in a horizontal scanning direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2015-012871, filed Jan. 27, 2015, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a lens mirror arrayconstituted by lenses and mirrors, an optical unit and an image formingapparatus.

BACKGROUND

Conventionally, an image forming apparatus (image reading apparatus)such as a scanner, a copier, an MFP (multi-function peripheral) and thelike, uses a lighting device and a lens array in which a plurality oflenses is arranged to form an image of a document on an image sensor andread the document image. Further, in an image forming apparatus such asa printer, a copier, an MFP (multi-function printer) and the like, usinga light-emitting element such as LED and the lens array, light ray fromthe LED is imaged on a photoconductive drum through the lens array toform (expose) an image on the photoconductive drum. The lens array isconstituted by combining a plurality of lenses with apertures.

However, if an optical axis between lenses through which a light raypasses deviates, the light ray enters into a lens or mirror of nextelement to generate stray light, and thus imaging property and lightintensity variation of the lens array are greatly deteriorated. When aplurality of lenses and apertures are combined together, property of thelens array is deteriorated due to deviation at the time of assembly.

In Japanese Unexamined Patent Application Publication No. 2014-142449,an optical device (imaging element array) is disclosed in which a lensand a mirror are integrally molded to make deviation of the optical axisbetween the lens and the mirror small and a groove depth L of mirrorsurface is larger than a mirror width WO to reduce the stray light.However, as the groove depth L of mirror surface is larger than themirror width WO, the flow of resin during molding is worse and moldingtime becomes long. Alternatively, there is a problem that width ofprotrusion to pitch is narrow to reduce optical efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the structure of an image formingapparatus using an optical device according to an embodiment;

FIG. 2 is a diagram illustrating an enlarged image forming sectionaccording to the embodiment;

FIG. 3 is a diagram illustrating an enlarged image reading deviceaccording to the embodiment;

FIG. 4 is a perspective view of the optical device according to theembodiment;

FIG. 5 is a perspective view of an optical element according to theembodiment;

FIG. 6 is a perspective view of the optical element viewed from otherdirection according to the embodiment;

FIG. 7 is a diagram illustrating a state of input light and emissionlight of light ray corresponding to the optical element according to theembodiment;

FIG. 8 is a diagram illustrating each position of the optical elementaccording to the embodiment;

FIG. 9 is a diagram illustrating a cross-sectional distribution ofregular light and stray light and light to be stray light of eachposition shown in FIG. 8 of the optical element and position ofshielding film according to the embodiment;

FIG. 10 is a diagram illustrating a state when the optical element ismanufactured with an integral molding manner according to theembodiment;

FIG. 11 is a diagram illustrating the structure when an array body ismounted as a unit according to the embodiment; and

FIG. 12 is a diagram illustrating the unit structure of other example ofintegrating the optical device according to the embodiment.

DETAILED DESCRIPTION

In accordance with an embodiment, a lens mirror array is provided inwhich a plurality of optical elements, each of which comprises a firstlens surface configured to be formed at the top of convex portionprotruding outwards and converge light, a protrusion which includes afirst mirror surface configured to reflect the light emitted from thefirst lens surface at the top and a light-shielding surface configuredto have side walls at two sides thereof with respect to a lightadvancing direction and prevent advance of the light through the sidewalls, a second mirror surface configured to reflect the light reflectedby the first mirror surface of the protrusion and a second lens surfaceconfigured to image the light emitted from the second mirror surface onan image plane, is arranged in a horizontal scanning direction; and whenviewing surface of first lens surface side between the side-wallsurfaces of arranged adjacent optical elements in a horizontal scanningdirection, the protrusion keeps a predetermined distance with the firstlens surface nearby principal ray of the light emitted from the firstlens surface and is formed into a shape protruding towards the firstlens surface side.

Hereinafter, the embodiment is described with reference to theaccompanying drawings. The same reference numerals are applied to thesame components in each figure.

FIG. 1 is a diagram illustrating the structure of an image formingapparatus using an imaging element array (optical device) of integrationof a lens and a mirror. In FIG. 1, an image forming apparatus 10 is, forexample, an MFP (multi-function peripheral), a printer and a copier. Inthe following description, the MFP is exemplified.

A document table 12 of transparent glass is arranged at the upperportion of a main body 11 of an MFP 10, and an ADF (automatic documentfeeder) 13 is arranged on the document table 12 to be opened and closed.An operation panel 14 is arranged at the upper portion of the main body11. The operation panel 14 includes various keys and a touch panel typedisplay section.

A scanner section 15 serving as a reading device is arranged at thelower portion of the ADF 13 in the main body 11. The scanner section 15reads a document sent from the ADF 13 or a document placed on thedocument table to generate image data and thus is provided with acontact-type image sensor 16 (hereinafter, simply referred to as “imagesensor”. The image sensor 16 is arranged in a horizontal scanningdirection (depth direction in FIG. 1).

The image sensor 16, in a case of reading an image of the documentplaced on the document table 12, reads the document image line by linewhile moving along the document table 12. The image sensor 16 isexecuted throughout whole document size to read the documentcorresponding to one page. In a case of reading an image of the documentsent from the ADF 13, the image sensor 16 is located at a fixed position(position shown in FIG. 1).

A printer section 17 is arranged at the center of the main body 11 and aplurality of cassettes 18 for housing papers of various sizes isarranged at the lower portion of the main body 11. The printer section17 includes a photoconductive drum and an optical scanning device forexposing the photoconductive drum. The optical scanning device, which isprovided with a scanning head 19 containing a LED serving aslight-emitting element, exposes the photoconductive drum with the lightray from the scanning head 19 to generate an image.

The printer section 17 processes image data read by the scanner section15 and image data created by a PC (personal computer) to form an imageon a paper serving as an image receiving medium. The printer section 17,which is, for example, a color laser printer in a tandem system,contains image forming sections 20Y, 20M, 20C and 20K of each color ofyellow (Y), magenta (M), cyan (C) and black (K).

The image forming sections 20Y, 20M, 20C and 20K are parallelly arrangedat the lower side of an intermediate transfer belt 21 along downstreamside thereof from upstream side thereof. The scanning head 19 alsoincludes a plurality of scanning heads 19Y, 19M, 19C and 19K in responseto the image forming sections 20Y, 20M, 20C and 20K.

FIG. 2 is a diagram illustrating an enlarged image forming section 20Kwithin the image forming sections 20Y, 20M, 20C and 20K. In thefollowing description, as each of image forming sections 20Y, 20M, 20Cand 20K has the same structure, the image forming section 20K isdescribed as a representation.

As shown in FIG. 2, the image forming section 20K includes aphotoconductive drum 22K serving as an image carrier. A charging charger23K, a developing device 24K, a primary transfer roller 25K, a cleaner26K and a blade 27K are arranged around the photoconductive drum 22Kalong a rotation direction t. An exposure position of thephotoconductive drum 22K is irradiated with light from the scanning head19K to carry an electrostatic latent image thereon.

The charging charger 23K of the image forming section 20K uniformlycharges the whole surface of the photoconductive drum 22K. Thedeveloping device 24K supplies two-component developing agent consistingof black toner and carrier to the photoconductive drum 22K through adeveloping roller 24 a to which developing bias is applied to form atoner image on the photoconductive drum 22K. The cleaner 26K, using theblade 27K, removes the toner left on the surface of the photoconductivedrum 22K.

As shown in FIG. 1, a toner cartridge 28 for supplying the toner to thedeveloping devices 24Y-′24K is arranged at the upper portion of theimage forming sections 20Y-20K. The toner cartridge 28 contains tonercartridges (28Y-28K) of each color of yellow (Y), magenta (M), cyan (C)and black (K).

The intermediate transfer belt 21 is stretched by a driving roller 31and a driven roller 32 and moves cyclically. The intermediate transferbelt 21 is opposite to the photoconductive drums 22Y-22K in contact witheach other. As shown in FIG. 2, a primary transfer voltage is applied toa position where the intermediate transfer belt 21 faces thephotoconductive drum 22K through a primary transfer roller 25K and thetoner image on the photoconductive drum 22K is primarily transferredonto the intermediate transfer belt 21.

A secondary transfer roller 33 is arranged to face the driving roller 31which stretches the intermediate transfer belt 21. At the time a paper Spasses through a position between the driving roller 31 and thesecondary transfer roller 33, a secondary transfer voltage is applied tothe paper S through the secondary transfer roller 33. Then the tonerimage on the intermediate transfer belt 21 is secondarily transferredonto the paper S. A belt cleaner 34 is arranged nearby the driven roller32 of the intermediate transfer belt 21.

As shown in FIG. 1, a conveyance roller 35 for conveying the paper Staken out from a paper feed cassette 18 is arranged between the paperfeed cassette 18 and the secondary transfer roller 33. Further, a fixingdevice 36 is arranged at the downstream side of the secondary transferroller 33.

A conveyance roller 37 is arranged at the downstream side of the fixingdevice 36. The conveyance roller 37 discharges the paper S to a paperdischarge section 38. A reverse conveyance path 39 is arranged at thedownstream side of the fixing device 36. The reverse conveyance path 39reverses the paper S and guides the reversed paper S in a direction ofthe secondary transfer roller 33, and thus the reverse conveyance path39 is used at the time of a duplex printing.

Next, the structure of the scanning head 19K of the optical scanningdevice is described with reference to FIG. 2. The scanning head 19K isopposite to the photoconductive drum 22K to expose the photoconductivedrum 22K. The photoconductive drum 22K can rotate at a preset rotationspeed to store charge on the surface thereof and the photoconductivedrum 22K is irradiated with the light from the scanning head 19K andexposed to form the electrostatic latent image on the surface thereof.

The scanning head 19K includes an optical device 50 which is abuttedagainst a dustproof cover glass 44 and supported by a holder 41. At thebottom of the holder 41, a support 42 is arranged on which LED element43 serving as light-emitting element is arranged. The LED elements 43are arranged linearly at equal intervals in a horizontal scanningdirection. A substrate (not shown) containing a driver IC forcontrolling the light emitting of the LED element 43 is arranged in thesupport 42. The detailed structure of the optical device 50 is describedlater.

The driver IC, which constitutes a control section, generates a controlsignal of the scanning head 19K based on the image data read by thescanner section 15 and the image data created by the PC to enable theLED element to emit light with a predetermined amount of light under thecontrol of the control signal. Light ray emitted from the LED element 43enters into the optical device 50 and is imaged on the photoconductivedrum 22 k through the optical device 50 to form the image on thephotoconductive drum 22 k. The cover glass 44 is installed at the upperportion (emission side) of the scanning head 19K.

FIG. 3 is an illustration diagram illustrating the structure of theimage sensor 16 of the scanner section 15 (reading device). The imagesensor 16 reads an image of a document placed on the document table 12or an image of a document fed by the ADF 13 according to the operationof the operation panel 14. The image sensor 16 is a one-dimensionalsensor arranged in a horizontal scanning direction and contains ahousing 45.

The housing 45 is arranged on a substrate 46. Two LED line lightingdevices 47 and 48 for emitting the light in a direction of the documentare arranged on the surface of the housing 45 at the document table 12side in a manner of extending in a horizontal scanning direction (depthdirection of FIG. 3). The LED line lighting devices 47 and 48 areequipped with LED and a light guide body. Light source is not limited tothe LED and may be a fluorescent tube, a xenon tube, a cold cathode tubeor an organic EL.

The optical device 50 described later is supported between the LED linelighting devices 47 and 48 at the upper portion of the housing 45 and asensor 49 constituted by CCD, CMOS and the like is mounted on thesubstrate 46 in the bottom of the housing 45. A light shield 52 having aslit 51 is installed at the upper portion of the housing 45.

The LED line lighting devices 47 and 48 irradiate an image readingposition of the document placed on the document table 12 and the lightreflected by the image reading position enters into the optical device50 via the slit 51. The optical device 50 functions as an erectingequal-magnification lens. The light entering into the optical device 50is emitted from an emission surface of the optical device 50 and imagedon the sensor 49. That is, the reflection light reflected by thedocument within light emitted from the lighting devices 47 and 48 passesthrough the optical device 50. The imaged light, through the sensor 49,is converted into an electrical signal which is transferred to a memorysection (not shown) of the substrate 46.

Hereinafter, the structure of the optical device 50 is described indetail. The optical device 50 composes of optical elements which havethe same structure subjected to integral molding. FIG. 4 is aperspective view illustrating the optical device 50 according to theembodiment. The optical device 50 is manufactured by integrating aplurality of optical elements 55 arranged parallelly in a horizontalscanning direction and a flange section 56 arranged for handling easy betouched by a hand at the time of handling. Herein, the optical elementsarranged in a horizontal scanning direction as a whole are referred toas an optical element array body or a lens mirror array.

FIG. 5(a) is a perspective view of one optical element 55. FIG. 5(b) isa diagram illustrating the structure of a protrusion when the opticalelement 55 is cut off along line a-b shown in FIG. 5(a). FIG. 6 is aperspective view of the optical element 55 shown in FIG. 5(a) viewedfrom a direction indicated by an arrow G. The optical element 55, whichis formed integrally with light transmissive material (glass or resin),reflects the incident light through a mirror surface using totalinternal reflection or Fresnel reflection to reflect the light to guideit in a predetermined direction. In FIG. 6, incident direction of thelight is indicated by an arrow A and emission direction of the light isindicated by an arrow B. A surface for reflecting the light is referredto as a mirror surface.

The optical element 55, into which the light enters, is provided with afirst convex lens surface 61 of which the surface protrudes outwards, afirst mirror surface 62 for reflecting the incident light from the firstlens surface 61, a second mirror surface 63 for reflecting the lightreflected by the first mirror surface 62 once again and a second convexlens surface 64 protruding outwards for emitting the light reflected bythe second mirror surface 63. The first mirror surface 62 is a plane,and the first lens surface 61 and the second lens surface 64 are curvednot only in one direction but also in a direction orthogonal to theaxis. For example, if it is assumed that a light incident direction ofthe first lens surface 61 of FIG. 6 is z axis, a horizontal directionvertical to the z axis is x axis and a direction vertical to the z axisand the x axis is y axis, the first lens surface 61 is curved not onlyin y axis direction, but also in x axis direction. The second lenssurface also has the same kind of shape with the first lens surface.

Such a first lens surface 61 having a convex lens function is used tocollect the incident light as much as possible and to form anintermediate reverse image. Further the second lens surface 64 having aconvex lens function is used to form a reverse image of the intermediatereverse image formed by the first lens surface 61 to form an erectimage.

It is regarded that the optical element 55, which largely consists of afirst block 66 including the first lens surface 61, the first mirrorsurface 62 and a base 66 d and a second block 67 including the secondmirror surface 63, the second lens surface 64 and a base 67 d, can beformed by integrating these two blocks.

As the light ray input to the first lens surface 61 of the opticalelement 55 enters into a different optical element and reaches an imageplane to make imaging property deteriorated, it is called as straylight. The material of the optical element 55 is resin or glass withwhich the optical element 55 is formed.

In the first block 66, the first lens surface 61 thereof serving aslight incident surface is in front, and a surface 74 (light-shieldingsurfaces 72 a and 72 b described later are not contained) whichcorresponds to an aperture surface and the emission surface of the firstlens surface, and which is constituted by a plurality of surfacesindicated by a hatching of slashes in a direction of the upper right inFIG. 6, is formed into a shape in such a manner that the closer it is toa principal ray, the closer it becomes to the first lens surface side,and protrudes to be closest to the first lens surface side nearby theprincipal ray emitted from the first lens surface 61. Thus, the surface74 includes a cutout portion 71 of obtuse angle approximate to rightangle nearby the principal ray emitted from the first lens surface 61and a protrusion 72 with a height L (recorded in FIG. 5(b)) in the lightincident direction at the center of bottom of the cutout portion 71. Asshown in FIG. 5(b), two surfaces of the protrusion 72 arelight-shielding surfaces 72 a and 72 b and the top of the protrusion 72is the first mirror surface 62.

The light-shielding surfaces 72 a and 72 b are arranged to prevent asmuch as possible that the light entering into the first lens surface 61enters into an adjacent optical element as stray light and includedownward slopes (taper) as shown in FIG. 5(b) to improve a releaseproperty during molding.

For example, a light absorbing surface 73 is formed on the slope planeof the second block in a light advancing direction to the first mirrorsurface 62 of the first block. The light absorbing surface 73 isarranged to prevent as much as possible that the light transmitting thefirst mirror surface 62 is collided and dispersed in the second block tobecome stray light, the light reflected by the second lens surface 64 isreflected inside the lens array to become the stray light and they reachthe image plane.

The second block 67 includes the second mirror surface 63, the secondlens surface 64, a flange section 68 of the second lens surface 64 andthe base 67 d. The reflection surface of the second mirror surface 63 isformed into a rectangle curved inwardly, and into a shape curved insidenot only in a length direction but also in the vertical direction. Thereflection surface with such a shape is used to prevent as much aspossible that light reflected by the first mirror surface enters intothe second mirror surface of an adjacent optical element throughheightening the reflection surface peripheral, and to make emissionangle after reflection of light serving as stray light reflected by thesecond mirror surface of the adjacent optical element different fromthat after reflection of light serving as regular light reflected by thesecond mirror surface of the optical element similar to that having thefirst mirror surface to create an area where the stray light and theregular light are separated spatially at the downstream side of thesecond mirror surface in the light path and in which a light-shieldingsection for shielding only the stray light and the light to be the straylight is set to shield only the stray light and the light to be thestray light without decreasing efficiency. The light converged by thesecond lens surface is converged in an image plane 69.

The light entering into the optical element 55 enters into the firstlens surface asymmetric in vertical scanning direction (y axisdirection), becomes light converged in both directions of horizontalscanning direction and vertical scanning direction and then enters intothe first mirror surface 62 at the top of the protrusion 72. As shown inFIG. 5(a), the light-shielding surfaces 72 a and 72 b are formed on theside walls of two sides of the protrusion 72 and the light collidingwith the light-shielding surfaces 72 a and 72 b is prevented fromadvancing.

The light of which advance is not prevented by the light-shieldingsurfaces 72 a and 72 b enters into the second mirror surface 63asymmetric in a direction vertical to the horizontal scanning direction.The light ray between the first mirror surface 62 and the second mirrorsurface 63 forms a reverse image. The light ray is reflected by thesecond mirror surface 63 and then guided to the second lens surface 64asymmetric in a direction vertical to the horizontal scanning direction.The light ray is imaged again by the second lens surface 64 to form anerecting equal-magnification image on the image plane 69.

Light-shielding films 61 n and 61 s are also arranged on the surface 74where the protrusion 72 is contacted with a part where the first lenssurface is arranged. The light-shielding films 61 n and 61 s are formedby, for example, UV ink.

The surface 74 keeps a predetermined distance with the first lenssurface 61 nearby the principal ray when seen from the horizontalscanning direction and protrudes towards the first lens surface 61 side.As shown in FIG. 7(b), the predetermined distance is a distance from apart where the surface 74 protrudes towards the first lens surface 61side of the side walls to a position where the light ray in a case inwhich an object point position in a horizontal scanning direction is ona surface containing the optical axis of the first lens surface ishardly shielded by the light-shielding surfaces 72 a and 72 b in thesame optical element 55 of the first lens surface 61.

In a case of the present embodiment, and when the object point is in theplane including the optical axis of the first lens surface in ahorizontal scanning direction, the principal ray appearing from thefirst lens surface 61 is almost coincident with the optical axis of thefirst lens surface 61.

FIG. 7(a) is a diagram illustrating transmission of the incident light,in the case in which an object point position in a horizontal scanningdirection is on a surface containing the optical axis of the first lenssurface, reflection and the path of the emission light viewing from theside surface of the optical element 55. FIG. 7(b) is a diagramillustrating transmission of the incident light, reflection and the pathof the emission light viewing from a cross-section of straight line A-Ashown in FIG. 7(a) of the optical element 55. The part protrudingtowards the first lens surface 61 side of the light-shielding surfaces61 n, 61 s, 72 a and 72 b hardly reduce the amount of light of theregular light at this optical element in such a manner that the lightray in a case in which the object point position in a horizontalscanning direction is on a surface containing the optical axis of thefirst lens surface is hardly shielded by the light-shielding surfaces 61n, 61 s, 72 a and 72 b in the same optical element 55 of the first lenssurface 61. The light ray is converged in the first lens surface, andthus the further the light ray goes away from the first lens surface,the smaller width in the horizontal scanning direction of the beam oflight is. Therefore, a range of position in the light advancingdirection of the part protruding towards the first lens surface 61 sideof the side walls is determined in response to the width of thelight-shielding protrusion 72.

FIG. 7(c), 7(d), 7(e), 7(f) are diagrams illustrating transmission ofthe incident fan rays including principal ray and extending in thehorizontal scanning direction, when the distance from a part where thesurface 74 protrudes towards the first lens surface 61 is changed. Label(d), (e), (f) shows each position of surface 74, and the label of thefigure illustrating transmission of the incident light, reflection andthe path of the emission light viewing from a cross-section of straightline A-A shown in FIG. 7(c) of the optical element 55.

The position according to the present embodiment, it is possible toavoid the decrease of the distance between the light-shielding surface74 and the first lens surface, is shown in FIG. 7(e). This is the samecondition as FIG. 7(b)

In case illustrated in FIG. 7(f), the distance from a part where thesurface 74 protrudes towards the first lens surface 61 is small. Theoutermost rays, which reaches imaging plane in FIG. 7(d), and FIG. 7(e),are shielded by the light-shielding films 61 s. In this case, theefficiency is smaller than case shown in FIG. 7(d) and FIG. 7(e).

In case illustrated in FIG. 7(d), the distance from a part where thesurface 74 protrudes towards the first lens surface 61 is larger than incase of FIG. 7(e). In this case, the efficiency is almost same as shownin FIG. 7(e). But the power of the stray light increases.

Through FIG. 7(a) and FIG. 7(f), it is understood that the incidentlight from the first lens surface 61 is reflected by the first mirrorsurface 62 at the top of the protrusion 72 and then condensed by thesecond lens surface 64 after reflected by the second mirror surface 63.However, the actual lens mirror array generates not only necessaryregular light but also unnecessary stray light.

In FIG. 7 (g) and FIG. 7 (h), the adjacent optical elements are alsoshown. FIG. 7 (g) shows the case that the object point position in ahorizontal scanning direction is on a surface containing the principalray passing through optical axis of the first lens surface. FIG. 7 (h)shows the case that the object point position in a horizontal scanningdirection is on a boundary surface of an element next to each other.

With the lens and mirror array of this constitution, the case that thereis at the position that an object point is shown in FIG. 7 (g) tends tocome to have a smallest light quantity.

In this embodiment in FIG. 7 (g), the center optical element, which issame as shown in FIGS. 7(b) and (e), focuses about 65% of all light raypower. Therefor increasing the power of center optical element describedbefore contributes increasing the all light beam power.

Next, FIG. 8 and FIG. 9 illustrate states of the abovementioned regularlight and the stray light and the light to be the stray light and thatobtained light serving as regular light is not shielded as much aspossible to shield only the stray light and the light to be the straylight.

In FIG. 8 and FIG. 9, a light-shielding surface 74′ shows a status of aplacement method of the conventional light-shielding section which isplaced in a plane vertical to the optical axis, which is different froma case in which the light-shielding surface 74 is formed into a shape insuch a manner that the closer the light-shielding surface 74 of thepresent embodiment is to the principal ray, the closer it is to thefirst lens surface side. In FIG. 8, the light-shielding surface 74′indicated by a thick dotted line is a surface vertical to the opticalaxis of the first lens surface, wherein distance between edge of thefirst lens surface 61 and edge of the light-shielding surface 74′, thatis, thickness of the edge (edge thickness) is similar to thickness ofedge in the case of the light-shielding surface 74 of the presentembodiment indicated by thick solid line. In this case, within the lightentering into the optical element 55, the closer the light-shieldingsurface 74 of the present embodiment is to the principal ray, the morethe light-shielding surface 74 protrudes towards the first lens surfaceside so that the shielded light by the light-shielding surface 74 is notshielded by the light-shielding surface 74′ and reflected by the firstmirror surface 62 and a second mirror surface 63 of the adjacent opticalelement and emitted from the second lens surface of the other opticalelement as the stray light.

Intensity distribution of the regular light at each position in a caseof the light-shielding surface 74 and in a case of the light-shieldingsurface 74′ is identical, which is shown in FIG. 7 (a).

FIG. 9 shows the intensity distributions of the regular light and thestray light and the light to be the stray light at each cross-sectionwhen the light-shielding surface 74′ with a placement method oflight-shielding section of conventional method is applied instead of thelight-shielding surface 74 and an area where the light is shielded bythe light-shielding surface 74 of the present embodiment at eachcross-section. The form of the light-shielding section in the exampleshows that the regular light when the light-shielding surface 74′ isapplied is not shield and only the stray light and the light to be thestray light generated at the time the light-shielding surface 74′ isapplied can be shielded.

FIG. 9(a) illustrates the intensity distributions of the regular lightof the cross-section at each of positions s1, s2, s3 and s4 of theincident light from the first lens surface 61 of the first block 66 whenthe light-shielding surface 74′ shown with the thick dotted line isassumed to be a surface vertical from the edge at the time thelight-shielding surface 74 is placed and the light shielding is started.FIG. 9 (b) illustrates the intensity distributions of the stray lightand the light to be the stray light of the cross-section at eachposition. These intensity distributions are simulation results.

The position s1 shows a position on the light path where the lightshielding is not carried out yet at the first lens surface 61 sidebetween side-wall surfaces for light-shielding, and the position s2shows a position on the light path where the light shielding begins tobe carried out through the light-shielding surface 74 with the structureof the embodiment at the first lens surface 61 side between side-wallsurfaces for light-shielding in the embodiment. Further, the position s3shows a surface which is vertical to the principal ray and containsstraight lines where the plane of the first mirror surface 62 intersectsthe light-shielding surface 74. The position s4 shows a positionslightly located at the upstream side of the light path of thelight-shielding surface 74′.

In FIG. 9(a) and FIG. 9(b), abscissa indicated by dashed line is theposition of the principal ray. Point area 91 is an area for indicatingthe existence of illumination by light which reaches to an image plane69, and slash area 92 therein indicates an area where illumination ismore than half of peak illumination of the point area 91.

In FIG. 9(a) and FIG. 9(b), thick frames s21, s22, s31, s32, s41 and s42drawn at two sides of each cross-sectional view in FIG. 9(a) and FIG.9(b) are cross-sections of the light-shielding surfaces 61 n, 61 s, 72 aand 72 b at the time of constitution of the embodiment, and the areabetween the line and vertical line indicating a boundary of the adjacentoptical element shows a block area of light at the time of constitutionof the embodiment. The block area changes at positions s2, s3 and s4,which is because the protrusion 72 is arranged obliquely with respect tothe principal ray and the light-shielding surface 74 is inclined fromthe surface vertical to the principal ray.

The regular light shown in FIG. 9(a) is vertically long at any ofpositions s1, s2, s3 and s4 if viewed from the cross-section, and thelight-shielding surfaces 61 n, 61 s, 72 a and 72 b are arranged to makethe regular light almost pass through at all the positions s1, s2, s3and s4.

On the other hand, the stray light and the light to be the stray lightshown in FIG. 9 (b) is an oblong if viewed from the cross-section, andis blocked at the side surface of the protrusion and the surface 74 bythe blocks s21, s22, s31, s32, s41 and s42 caused by the light-shieldingfilm.

The block areas s41 and s42 shows that the amount of light of theregular light does not be reduced and only the stray light and the lightto be the stray light is shielded. Moreover, the light shielded by theblock areas s21 and s22 is light advancing towards the center of theposition s4 in the horizontal scanning direction in FIG. 9 (b). Thus,the light obtained as stray light and light to be stray light can bealmost shielded by the light shielding of the block areas s21, s22, s31,s32, s41 and s42 and the downstream side thereof. On the other hand, atthe position s2, even if the side walls wholly shield lightcorresponding to part above the block areas s21 and s22, it isunderstood that the regular light is not almost shielded.

However, with such a structure, three risks are easy to occur,including: collapse of the shape of the first lens surface 61 due tovery short distance L between upper side of the first lens surface 61and upper side of the light-shielding surface 74 to cause insufficiencyof mechanical strength of the upper side of the first lens surface 61,prolongation of molding time due to deterioration of the flow of theresin during molding and occurrence of strain due to large difference ofthicknesses of the center and peripheral part of the lens to causedifference of heat shrinkage rate. Thus, it is desirable that thethickness from the first lens surface 61 to the surface 74 is identicalto that from the center of the first lens surface 61 in a y direction tothe lens edge as much as possible.

Further, it is desirable that the distance L at a position where thedistance between the first lens surface 61 and the light-shieldingsurface 74 is shortest is guaranteed to be such a degree that problemssuch as intensity and flow of the resin do not occur. On the basis ofit, in order to not only make the distance equal to distance to lenscenter but also suppress efficiently the occurrence of the stray light,it is desirable that the shape of the light-shielding surface 74 is ashape in which the first lens surface 61 moves parallelly in an opticalaxis direction.

A case in which the optical element 55 is integrally molded with thematerial such as resin is described with reference to FIG. 10. It isdesirable that excessive force is not applied to the first mirrorsurface and peripheral part thereof at the time cavity or core insert ispulled out during a process in which the first mirror surface ismanufactured more accurately through the integral molding. If the cavityor core insert is separated from the lens mirror array in a directionvertical to the first mirror surface, at a range close to the firstmirror surface, an under cut is generated in a part 101 indicated byslashes of FIG. 10 in order not to apply a shearing force to the firstmirror surface. Therefore, with further going towards the figure fromthe surface vertical to the first mirror surface 62, in a directionapproaching the first mirror surface, if there is a surface on which adraft taper 102 of 3-10 degrees is fixed, the undercut does not occur,and as the draft taper exists and large force is not applied to thesurface 74 at the time of opening mold, shape accuracy during moldingcan be improved easily.

A surface (surface formed by the light-shielding surface 61 s) oppositeto the first mirror surface between side-wall surfaces for lightshielding has a slope almost parallel to the first mirror surface at thefirst lens surface 61 side.

From the above, it is desirable that the shape of the boundary surfaceof the first lens surface 61 of the side walls is a protruded shape insuch a way as to have an angle about 3-10 degrees of 90 degrees positivedraft nearby the principal ray when viewed from the horizontal scanningdirection.

Herein, the protruded part is intersected with planes and is formed intoa smooth curved surface and a free-form surface to further suppress theamount of stray light.

FIG. 11 is a perspective view illustrating an example of the unitstructure at the time the optical device (lens mirror array) in whichthe abovementioned optical elements 55 are arranged in parallel is usedas the scanning head 19. A LED line array 111 in which LEDs are arrangedparallelly in a row is provided with LED light-emitting elements in ahorizontal scanning direction and irradiates light from lower part infigure.

A lens mirror array 112 in which the optical elements 55 are arranged isfixed and built in a housing 113. A hole is opened at the lower part infigure of the housing 113 and the light from the LED line array entersinto each of the optical elements 55.

A dustproof glass 114 is arranged on the housing 113. The dustproofglass 114 is pressed against the housing 113 through a plate spring 115.The plate spring 115 functions as a light-shielding member.

FIG. 12 is a cross-sectional view illustrating an example of the otherstructure in a case where the optical device of an example of thepresent invention is constituted as a LED print head.

Light from a LED print head 121 is emitted to the surface of aphotoconductive drum 120. A LED base 124 s is arranged on a supportmember 124 inside a housing 123 having a through hole 122 thereon. A LEDarray chip 125 connected with wirings on the LED base 124 s is arranged.

A lens array holder 127 having a through hole 126 thereon in figure isincorporated into the through hole 122. The abovementioned lens mirrorarray through which the light from the lower part passes is incorporatedinto the lens array holder 127 and a dustproof glass 128 is insertedbetween the through hole 126 and the lens mirror array. An incident sideaperture 129 is formed at the incident side of the optical element 55.

The surface of the rotating photoconductive drum 120 is irradiated withthe light passing through the optical element 55.

A plurality of LED elements is arranged parallelly in a horizontalscanning direction and each LED element emits and extinguishes lightbased on a printing signal obtained from the circuit of the LED base 124s. The LED array chip 125 in which a plurality of LED elements isarranged parallelly is installed on the LED base 124 s in accordancewith a printing width. Light entering into the incident side aperture129 at a predetermined angle in a vertical scanning direction isshielded with respect to the light emitted from the light-emitting LEDelements. After the unshielded light holds a predetermined propertythrough the optical element 55, the light serving as stray light isshielded by the lens array holder 127. The unshielded light is imaged asthe erecting equal-magnification image of LED light-emitting section onthe photoconductive drum 120.

For example, the LED elements with 42 μm pitch are arranged in the LEDprint head of 600 dpi in a horizontal scanning direction. These LEDelements emit and extinguish light according to the printing signal toform a latent image on the photoconductive drum 120.

After the dustproof glass 128, an array body 112 of the optical element55 and the incident side aperture 129 are inserted into the lens arrayholder 127, the array body 112 of the optical element 55 is applied witha predetermined pressure in the upper right of figure through a tool(not shown) and fixed in the lens array holder 127 through, for example,adhesive. Afterwards, the lens array holder 127 is adjusted to aposition corresponding to the housing 123 and then adhered.

The LED base 124 s on which the LED array chip 125 is installed is fixedon the support member 124. Further, the support member 124 is adjustedin such a manner that the image comes to a predetermined position, andthen fixed on the housing 123.

In accordance with the embodiment, the light-shielding surface 74 keepsa predetermined distance with the first lens surface nearby theprincipal ray and is formed into a shape protruding towards the firstlens surface, and thus compared with the conventional lens mirror array,the abovementioned lens mirror array enables the stray light not toescape to reduce aspect ratio of convex light-shielding section. Thepredetermined distance is a distance from a part where the surface 74protrudes towards the first lens surface 61 side of the side walls to aposition where the light ray in a case in which the object pointposition in a horizontal scanning direction is on a surface containingthe optical axis of the first lens surface is not shielded by thelight-shielding surfaces 72 a and 72 b.

In this way, through reducing the aspect ratio of the convexlight-shielding section, the flow of the resin during molding may beexcellent when the lens mirror array is manufactured by integralmolding, and thus it is possible to shorten the molding time. Otherwise,it is possible that the width of the protrusion to the pitch isincreased so as to improve optical efficiency.

In a case of the light-shielding surface 74′ with the conventionalmethod, distance between the surface (surface orthogonal to principalray axis) between side wall part and end part of optical elementsadjacent to two sides of the first mirror surface and the first lenssurface is reduced at edge. However, at all the positions according tothe present embodiment, it is possible to avoid the decrease of thedistance between the light-shielding surface 74 and the first lens,surface, and thus, the risk of colliding the shape of the first lenssurface can be reduced. In accordance with the embodiment, by moldingthe lens and the mirror integrally, the deviation of the optical axisbetween the lens and the mirror is reduced and thus, a lens mirrorarray, an optical unit and an image forming apparatus with excellentformability, high optical efficiency and less stray light can beobtained.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the invention. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinvention. The accompanying claims and their equivalents are intended tocover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A lens mirror array, wherein a plurality ofoptical elements, which comprises a first lens surface configured to beformed at the top of convex portion protruding outwards and convergelight, a protrusion which includes a first mirror surface configured toreflect the light emitted from the first lens surface at the top and alight-shielding surface configured to have side walls at two sidesthereof with respect to a light advancing direction and prevent advanceof the light through the side walls, a second mirror surface configuredto reflect the light reflected by the first mirror surface of theprotrusion and a second lens surface configured to image the lightemitted from the second mirror surface on an image plane, is arranged ina horizontal scanning direction; and when viewing surface at the firstlens surface side between the side-wall surfaces of arranged adjacentoptical elements in a horizontal scanning direction, the protrusionkeeps a predetermined distance with the first lens surface nearbyprincipal ray of the light emitted from the first lens surface and isformed into a shape protruding towards the first lens surface side. 2.The lens mirror array according to claim 1, wherein, a light-shieldingfilm is formed on the side walls at two sides of the protrusion and onthe surface of the surface of the first lens surface side between theside-wall surfaces of the adjacent optical elements.
 3. The lens mirrorarray according to claim 2, wherein the light-shielding film is coatedwith UV ink to be formed.
 4. An optical unit, comprising: a light sourcearray configured to be provided with light source to emit light; and alens mirror array in which a plurality of optical elements, whichcomprises a first lens surface configured to be formed at the top ofconvex portion protruding outwards and converge the light emitted fromthe light source array, a protrusion which includes a first mirrorsurface configured to reflect the light emitted from the first lenssurface at the top and a light-shielding surface configured to have sidewalls at two sides thereof with respect to a light advancing directionand prevent advance of the light through the side walls, a second mirrorsurface configured to reflect the light reflected by the first mirrorsurface of the protrusion and a second lens surface configured to imagethe light emitted from the second mirror surface on an image plane, isarranged in a horizontal scanning direction; and when viewing surface atthe first lens surface side between the side-wall surfaces of arrangedadjacent optical elements in a horizontal scanning direction, theprotrusion keeps a predetermined distance with the first lens surfacenearby principal ray of the light emitted from the first lens surfaceand is formed into a shape protruding towards the first lens surfaceside.
 5. An image forming apparatus, comprising: a light source arrayconfigured to be provided with light source to emit light; a lens mirrorarray in which a plurality of optical elements, which comprises a firstlens surface configured to be formed at the top of convex portionprotruding outwards and converge the light emitted from the light sourcearray, a protrusion which includes a first mirror surface configured toreflect the light emitted from the first lens surface at the top and alight-shielding surface configured to have side walls at two sidesthereof with respect to a light advancing direction and prevent advanceof the light through the side walls, a second mirror surface configuredto reflect the light reflected by the first mirror surface of theprotrusion and a second lens surface configured to image the lightemitted from the second mirror surface on an image plane, is arranged ina horizontal scanning direction; and when viewing surface at first lenssurface side between the side-wall surfaces of arranged adjacent opticalelements in a horizontal scanning direction, the protrusion keeps apredetermined distance with the first lens surface nearby principal rayand is formed into a shape protruding towards the first lens surfaceside; a photoconductor configured to include a photoconductive surfaceon the image plane to form an latent image thereon; and a developingsection configured to visualize the latent image formed on thephotoconductor.